An antenna tuner is a device connected between a radio frontend electronics (transmitter and/or receiver) and its antenna to improve power transfer between them by matching the impedance of the radio frontend electronics to the antenna. An antenna's impedance can be different at different frequencies and influenced by object close-by. An antenna tuner matches a radio frontend electronics with a fixed impedance (typically 50 Ohms for modern transceivers) to the impedance of the antenna, which is influenced by human contact or objects in proximity, thus different from the impedance of the transceiver. There are many different implementations of antenna tuners using broadband matching, narrow band design, or other complex designs.
For mobile wireless devices, closed-loop antenna tuning (CLAT) can extend battery life and improve user experience by monitoring the antenna impedance changes and adjusting the tuner state to achieve improved matching. For example, the RF performance due to mismatch between the antenna and the transceiver cause a power loss of approximately −1 dB, human body phantoms (e.g., head and hand) cause another −3 dB power loss, and real-life (e.g., many user conditions) cause up to −7 dB power loss. In order to maximize the delivered power from the source (radio transceiver) to the load (antenna), or vice versa, maximum transducer gain of the antenna is desired. To implement closed-loop antenna tuner, a coupler between the radio frontend electronic and antenna is typically incorporated to sample the RF path signal in both the forward (radio frontend electronics to antenna) and reverse direction (antenna to radio frontend electronics. By comparing forward path signal and reverse path signal, the reflection coefficient can be estimated. The CLAT searching algorithm thus involves searching an optimal antenna tuner setting to maximize the transducer gain of the antenna.
The current CLAT searching algorithm has several issues. The tuner has a large number of settings (e.g., half a million states). First, the gradient-type search method might converge on local optimum, not global optimum. Second, extensive search is computational intensive. Third, the simplified search still requires 1K to 4K iterations. A simplified CLAT search algorithm with global optimum is sought.